Treatment of high boiling catalytically cracked products with activated carbon



g- 19, 1953 J. REHNER, JR, ETAL 2,8 TREATMENT OF HIGH BOILING CATALYTICALLY CRACKED PRODUCTS WITH ACTIVATED CARBON Filed July 16, 1953 FRACTIONATOR JOHN REHN R JR LAWRENCE .EBY '"VENToRS TREATMENT OF HIGH BOILING CATALYTI- CALLY CRACKED PRODUCTS WITH ACTI- VATED CARBON John Rehner, Jr., Westfield, and Lawrence T. Eby, Linden, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application July 16, 1953, Serial No. 368,256 3 Claims. (Cl. 196-52) This invention concerns a novel refining process of application to high boiling catalytically cracked oils. The process of this invention is applied to catalytically cracked products boiling above about 700 F. The process entails the treatment of oils of this character with activated carbon in order to minimize the carcinogenicity of these oils and to improve their value as ultimate products or for further processing.

In the catalytic cracking process, petroleum fractions are heated in the presence of a catalyst and large petroleum molecules are broken down into small molecules providing products such as gasoline, kerosene, home heating oils and diesel oils. However, in the catalytic cracking process there is a residual material which contains high boiling constituents including a substantial concentration of high boiling polycyclic aromatic hydrocarbons. High boiling residual material of this character is frequently used for industrial fuels.

Because the residual fractions of catalytic cracking referred to contain polycyclic aromatic hydrocarbons, it was suspected that this material might be carcinogenic in character. At this date it has been established that this is the fact, at least as applied to lower animals. Furthermore, this has been borne out by a limited amount of information indicating that direct contact with certain higher boiling petroleum fractions has caused occupational cancer in man. As a result of this discovery, it has become important to provide all possible safeguards to prevent any possibility for the occurrence of cancer due to contact with high boiling catalytically cracked products.

This problem has heretofore been met by economically expensive expedients. For example, it has been recommended that the high boiling catalytically cracked residues which are suspected of being carcinogenetic should be blended with noncareinogenic products so as to include no more than 10% of the carcinogenic fraction; such blends have been shown to be safe. This has created some problem in the disposal of the heavy residues from catalytic cracking and has caused a considerable loss in the economic value of the residual cracked products.

Since this problem was first recognized, it has been appreciated that some technique should be found for minimizing the carcinogenicity of heavy catalytically cracked residues. Such methods should be employed in order to minimize the occupational hazard of handling or processing such stocks and in order to eliminate need for the more expensive safety expedients heretofore used. The present invention is directed to this purpose and for the first time provides a practical and eflicient process for reducing the carcinogenicity of heavy catalytically cracked residues.

The process of this invention is a relatively simple process requiring contact of the heavy catalytically cracked oils with activated carbon. The term activated carbon is used as conventionally understood in the art to identify a char which has been treated by oxygen, steam or the nite States Patent ICC like to activate it. The activating process is operative to produce a multitude of fine pores in the char to provide the article of commerce known as activated carbon. The process of this invention is based on the discovery that unlike other solid'adsorbents, activated carbon has the property of effectively removing carcinogens from heavy oils.

In order to carry out the process of this invention, it is necessary to intimately contact activated carbon with the heavy catalytically cracked oils. Contact may be carried out by mixing the activated carbon in the oil as a slurry. About 2 to 20 weight percent treat of activated carbon is required for the purposes of this invention. The precise treat to be used will depend upon the carcinogenicity of the material to be treated. In general in the treatment of the heavy residues from catalytic cracking about 10 to 20 weight percent of activated carbon is preferably employed. The contact conditions are to be adjusted to permit the adsorption achieved to approach equilibrium conditions. For this purpose it is preferred to use elevated contacting temperatures preferably in the range of about 400 to 600 F. Temperatures in this range also have the virtue of reducing the viscosity of the heavy oils sufiiciently to facilitate handling and processing. Temperatures outside this range may be employed with corresponding adjustment of the time required to reach equilibrium. At temperatures in the range indicated, the desired adsorption with activated carbon occurs readily, generally requiring a contact time of somewhat less than about 30 minutes. Pressure does not materially affect the adsorption process so that any desired pressure may be employed during contacting. If desired, a diluent may be employed to decrease the viscosity of the oil to be treated. Diluents are preferably low molecular weight paraffinic hydrocarbons such as the C to C parafiins. Thus, for example, normal heptane is a desirable compound to employ as a diluent and may be mixed with the heavy catalytic oils in proportions of about 10 to 50%.

After contacting of the catalytic oils with the activated carbon in this manner, the adsorbent may be separated from the oil by filtration, centrifuging, settling or the like. Traces of oil may be removed from the adsorbent by washing with a low molecular weight hydrocarbon of the nature which may be employed as a diluent. The diluent and/or wash hydrocarbon may be removed from the final oil product by a simple fractionation operation. The oil product resulting from this treatment is a heavy catalytically cracked oil which has been rendered substantially inactive as regards carcinogenicity. The inspections of this product closely correspond to those of the untreated oil. However, the process is effective to remove a substantial portion of the high boiling polycyclic aromatic compounds originally present in the oil.

The accompanying drawing diagrammatically illustrates an embodiment of the invention showing the overall processing of petrolelnn fractions resulting in the formation of carcinogenic products and permitting the elimination of the carcinogenic components in accordance with this invention.

A conventional catalytic cracking system is illustrated in the drawing including the cracking zone 1, the catalyst regenerator 2 and the product fractionator 3. While it will be understood that this invention is of application to catalytically cracked products however obtained, the process illustrated is a fluidized catalytic cracking operation. In this process conventional and well-known cracking catalysts may be used such as silica-alumina mixtures, silica-magnesia mixtures, montmorillonite clay, and the like. In the particular process illustrated, a gas oil feed stock may be introduced to the cracking zone through line 4. This is brought into the reaction zone 1 through 1 a suitable distributing grid so as to be brought in contact with a mass of cracking catalyst maintained in fluidized condition in the cracking zone 1. For this purpose, particles of cracking catalyst of suitable size are employed and the ratio of oil to catalyst is maintained so as to permit the establishment and maintenance of a fluidized condition. In this condition, up-flowing oil vapors passing through the catalyst particles cause the catalyst to have the general characteristics of a liquid. Thus, the catalyst bed is characterized by an upper surface and has the general hydraulic properties of a liquid. During passage through the cracking zone at a temperature of about 800 to 1000 F., the oil feed stock undergoes the cracking reaction and the cracked products may be removed overhead through line 5. As will be described, these cracked products are subjected to fractionation in the fractionation zone 3.

Cracking catalyst is continuously withdrawn from the fluidized bed of catalyst in zone 1 through line 6. Air is introduced to intersecting conduit 7 so as to force the catalyst upwardly into the regeneration zone 2. In the presence of the air carbonaceous impurities are oxidized in zone 2 so as to regenerate the catalyst. The products of this oxidation are removed overhead through lines 8 and 9,, while the regenerated catalyst is withdrawn from the regenerate-r through line 10 for recycle to the cracking zone through line 4.

It is not considered necessary to further describe the catalytic cracking operation identified since this is not a part of the present invention. As indicated, however, regardless of the manner of carrying out the catalytic cracking reaction, a cracked product stream is obtained which is fractionated in a distillation tower such as fractionator 3 illustrated. In fractionation zone 3 the catalytically cracked products are separated so as to permit a withdrawal of gaseous products from the uppermost portion of the fractionator through line 11. Light boiling, liquid products such as gasoline may be withdrawn from suitable side stream withdrawals such as line 12, Higher boiling products are withdrawn from other withdrawals positioned at lower portions of the fractionator and from the bottom Withdrawal of the fractionator. For example, fractionator 3 may be operated to permit withdrawal of a side stream through line 13 boiling above 700 F. Such a side stream is commonly identified as cycle oil. Still heavier boiling residual products of cracking are then withdrawn from the lowest portion of the fractionator through bottom withdrawal 14. The bottoms product will contain small proportions of catalyst particles carried over from the cracking zone. Consequently, the fraction is passed to a settling zone 15 permitting withdrawal of a clear or clarified slurry oil through line 16.

As described, fractionator 3 is operated to permit segregation of the portion of the cracked products boiling above 700 F. This particular fraction of the cracked products isspecificd since it has been established that the portion of the cracked products boiling below 700 F. is non-carcinogenic. For this reason, the process of this invention is applied to the products Withdrawn from the fractionator through line 13 and 14 boiling above 700 F. Sharp fractionation is not required however, and lower boiling constituents may be included.

Either or both of the product streams of lines 13 and 14 may be processed. As illustrated, these product streams may be combined and passed together to the activated carbon treatment zone 17. As indicated, it is preferred to carry out contact of the oil with activated carbon at elevated temperatures. The catalytic oil may therefore be passed through a preheater 19 prior to introduction to adsorbent treating zone 17. In addition, suitable heating coils 20 may be maintained in zone 17 or other heating provisions may be made. Activated carbon may be introduced to the treating zone through solids transfer line 18. Mixing of the activated carbon '4 with the oil may be secured by use of mechanical agi tators or by the bubbling of air or inert gas through the oil. In the event a diluent is employed during the activated carbon treatment, this diluent may be brought into zone 17 through line 32.

The activated carbon treatmentmay be carried out on a batch or continuous basis provided the treatment period be about 15 minutes to 2 hours. After this contacting period, the slurry of activated carbon in oil may be removed by means of line 30 from zone 17 to a settling zone 22. In zone 22 the oil is permitted to remain in a quiescent state so that the activated carbon may settle from the oil. The final oil product may then be withdrawn through line 23 and the activated carbon may be removed from the settling zone through line 24. As indicated, if desired, the separated activated carbon can be washed with a paratfinic hydrocarbon to recover residual traces of the treated catalytic oil.

In the event a diluent is employed in the activated carbon treatment, this diluent may be removed from the final oil product by a simple stripping operation.

The oil product of line 23 is rendered substantially inactive or non-carcinogenic by the treatment described. This oil product may therefore be used as fuel oil or may be used for other purposes Without danger. However, it is a particular feature of this invention that this oil product be recycled to the catalytic cracking zone 1. The oil product, by virtue of the removal of carcinogenic polycyclic aromatic hydrocarbons, is greatly improved as a cracking feed stock. For this reason, it becomes attractive to recycle this product for further catalytic cracking. In this connection it is well-known that clarified oil from a catalytic cracking process is sufiiciently refractory so as to discourage recycle cracking of this stock. This is particularly true in view of the fact that recycle cracking of a conventional clarified oil does not serve to eliminate the carcinogenicity of this material. In other words, the polycyclic aromatic hydrocarbons which are objectionable are not entirely cracked in recycle cracking Which may result in a further build-up in the cracked products of these carcinogenic materials. However, heavy catalytically cracked fractions which have been treated with activated carbon as described are not subject to these disadvantages and constitute good "crackiug feed stocks. Furthermore, the removal of the polycyclic aromatic components results in less carbon deposition by the recycled oil on the cracking catalyst, and hence a more efficient catalytic cracking process. It therefore becomes practical and desirable to employ recycle cracking to substantially eliminate or to greatly minimize the final heavy residue obtained from the overall process. By this means the cycle oil and slurry oil are effectively upgraded to the more valuable heating oil and fuel fractions.

In order to full demonstrate the nature and advantages of this invention, reference will be made to typical experiments which were conducted to evaluate the invention. In basic work which was carried out it was determined that the carcinogens present in heavy catalytic oils are primarily polynuclear aromatic hydrocarbons which may or may not have a small number of low molecular weight alkyl groups attached to the aromatic nuclei. It would be expected that compounds of this character could be separated from catalytic oils by treatment with solid adsorbents. Thus, it is generally expected that solid adsorbents such as silica gel, alumina, clay, activated carbon and the like will serve to segregate aromatic hydrocarbons from other hydrocarbon types. In order to evaluate this possibility, tests were conducted in which 5 g. of an aromatic fraction from heavy catalytic oil was chromatographed through 600 cc. of solid adsorbent. Such tests were carried out employing silica gel, alumina, the type of activated carbon known as Nuchar C, bauxite, magnesium silicate marketed as Magnesol A, and fullers earth. Difference solvents were employed in an elution technique to desorb the constituents of the oil. In these experiments the adsorbent was contained in a column into which the aromatic oil and the developing solvents were passed by gravity flow. The difierent developing solvents were employed in 800 cc. portions. These solvents are identified in Table I.

Table I 1. n-heptane 2. 1% benzene-99% n-heptane 3. 2% benzene-98% n-heptane 4. 4% benzene-96% n-heptane 5. benzene-90% n-heptane 6. 20% benzene-80% n-heptane 7. 50% benzene-50% n-heptane 8. Benzene 9. Pyridine In order to evaluate the separation attained by this process, the fractions separated by the various eluates were subjected to ultraviolet examination. The spectra of each of the fraction isolated were obtained.

It was found that these solvents effected complete removal of all polynuclear aromatic hydrocarbons from these adsorbents, with the exception of the activated carbons. In the case of activated carbon only 33% of the aromatic oil was removed by the solvents, and the removed fraction contained only benzene and naphthalene nuclei, no higher polynuclear species being detectable.

Further experiments conducted to verify this result indicated that, in fact, activated carbon has the unique property, among other adsorbents, to hold polynuclear aromatic hydrocarbons very tenaciously. The experiments conducted indicated that with the exception of activated carbon the adsorption apparently occurs by polar attractions. Activated carbon on the other hand apparently separates high molecular weight aromatic compounds by other adsorptive powers, apparently relating to the molecular size and shape of the particular hydrocarbon.

A number of commercial adsorbents, including those generally used for decolorization of petroleum oils, and also two activated carbons, were used in simple single stage contacting experiments with a heavy catalytic oil. The oil was stirred with the specified weight percent of adsorbent while heating to 200 C. in about 24 minutes. This mixture was then cooled to 100 C. in about 13 minutes and filtered. An examination of the spectra of these treated samples showed that the activated carbon was no more effective in decolorization or in changing the shape of the spectral curve than were some of the other adsorbents, as shown in Table II.

Table II Wt. Optical Absorptivity at Ratio of Per- Absorp Absorbent cent tivity at of Ad- 420 430 440 500 440/430 sorbent my m my m my None 0 346 256 219 048 86 Hyfio (diatomaceous silica filter) 10 350 258 227 .052 88 Pumice 10 343 250 215 048 86 Attapulgus Fines (clay) 1O 252 179 156 029 87 Activated Alumina 10 .270 195 .167 029 86 Super Filtrol (activated clay) 10 173 128 119 020 93 Silica Gel (28-200 mesh 10 240 187 171 040 .91 desiccant) 20 167 129 125 .030 97 Santocel 58 (silica aerogel)- 10 266 192 165 .030 86 Santccel 45 (silica aerogel)- 10 219 156 138 021 88 Magnesol (magnesium 10 153 111 108 014 97 silicate) 20 090 067 072 007 1. 08 Magnesol A (magnesium silicat 10 150 108 104 015 96 Merck activated charcoaL 10 166 117 101 019 S6 w e-t 18 :Hi 1a 1. .22 18%? 1e The best decolorizing adsorbent for this heavy catalytic oil was Magnesol. Its efiectiveness in reducing carcinogenicity was therefore compared with that of the activated carbon, Norite A, by carrying out animal tests on the above two oil samples treated with 20% of these two adsorbents. The tests conducted were carried out according to the procedure described in the paper Properties of High Boiling Petroleum Products by Dietz, King, Priestley and Rehner, published in Industrial and Engineering Chemistry, volume 44, page 1818. This procedure permits of identification of the carcinogenicity of a sample by determination of the tumor potency in carefully controlled tests with mice. In the scale employed, tumor potency values of 50 or 60 are considered high, while values of about 30 or less are marginal and commonly indicate that only benign tumors would result.

In these tests the sample of catalytic oil employed was the fraction of a commercially cracked product containing 60% of material boiling above 700 F. This product was treated with magnesium silicate and activated carbon in the two experiments described above. In each case 20 weight percent treat of the adsorbent was employed at a treating temperature of about 200 C. for a period of about one-half hour. The treated -oil was separated from the adsorbent by filtration.

It was found that the untreated catalytic oil had a tumor potency value of 54. The oil treated by magnesium silicate had a tumor potency value of 39, indicating some elimination of carcinogens, but providing a final product which would still be objectionable. Finally, it was found that the sample treated with activated carbon had a tumor potency value of only 13. Since a completely inactive sample has a tumor potency value of 10, it is apparent from this data that the process of this invention serves to substantially inactivate a carcinogenic oil.

What is claimed is:

1. A catalytic cracking process comprising the steps of catalytically cracking a petroleum feed stock to form a cracked product, segregating a fraction boiling above about 700 F. from said product, passing said fraction to a treating zone, contacting said fraction in liquid form with from about 2% to about 20% by weight of activated carbon to form a treated liquid phase from which carcinogenic compounds have been removed, and separating said treated phase from said activated carbon.

2. The process defined by claim 1 in which the said contact is carried out for a period of about 15 minutes to 2 hours at a temperature in the range of about 200 to 600 F.

3. The process according to claim 1 wherein said treated phase is recycled to the catalytic cracking operation.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Smith et al.: AMA Arch. Indust. Hyg. 4; 299 to 314, 1951 National Institute of Health Library.

Brewster: Organic Chemistry, second edition, Prentice- Hall Inc., 1953, p. 704. 

1. A CATALYST CRACKING PROCESS COMPRISING THE STEPS OF CATALYTICALLY CRACKING A PETROLUM FEED STOCK TO FORM A CRACKED PRODUCT, SEGREGATING A FRACTION BOILING TO FORM ABOUT 700*F. FROM SAID PRODUCT, PASSING SAID FRACTION TO A TREATING ZONE, CONTACTING SAID FRACTION IN LIQUID FORM WITH FROM ABOUT 2% TO ABOUT 20% BY WEIGHT OF ACTIVATED CARBON TO FORM A TREATED LIQUID PHASE FROM WHICH CARCINOGENIC COMPOUNDS HAVE BEEN REMOVED, AND SEPERATING SAID TREATED PHASE FROM SAID ACTIVATED CARBON. 